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| Dissertation / PhD Thesis/Book | PreJuSER-37424 |
2003
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/223
Report No.: Juel-4004
Abstract: In conclusion we would like to present a short list of the main results obtained in the thesis. $\bullet$ A detailed theoretical analysis of the different channels of the reaction NN $\rightarrow$ NN$\eta$, i.e. pp $\rightarrow$ pp$\eta$, pn $\rightarrow$ pn$\eta$ and pn $\rightarrow$ d$\eta$, has been performed in the near-threshold region, i.e. for the energy not more than 50 MeV above threshold. The production mechanisms which have been included consist of re-scattering terms with M = $\pi, \rho, \eta, \sigma$ meson exchanges and the direct $\eta$ production. Effects of the final and initial state interaction between the nucleons are fully taken into account. The calculation utilizes the Bonn B and the CCF NN models for the treatment of the FSI and ISI, respectively, and a realistic coupled-channel model of the $\pi$N system developed in Jülich, which was used for the calculation of the MN $\rightarrow$ $\eta$N transition amplitudes. A quantitative agreement of calculated cross sections with the experimental data is achieved for all channels of this reaction. $\bullet$ It is found that the leading role in the process of the $\eta$-meson production near threshold belongs to the re-scattering mechanism with the intermediate pion exchange. The contributions from other meson exchanges, specifically from $\rho$ and $\eta$ as well as from the direct $\eta$ production are smaller. However, they are still important and have to be taken into account because of their influence on the cross sections due to the interference with the amplitude corresponding to the $\pi$ exchange. $\bullet$ NN FSI effects in the reactions NN $\rightarrow$ NNM with production of M but with different masses are studied in detail. It is demonstrated that the full reaction amplitude can not be factorized on the pieces corresponding the production process and independently the NN FSI if one is interested in the quantitative predictions for the cross sections. It is shown that the use ofthe Jost function for the evaluation of NN FSI effects leads to the results considerably different from the ones of correct calculation. It is shown also that NNFSI effects are not universal with respect to the different produced mesons, i. e. their absolute values definitely depend on the mass of the produced meson (momentum transfer). $\bullet$ It is found that ISI effects in the reaction NN $\rightarrow$ NN$\eta$ are not universal with respect to the defferent meson exchanges, i. e. to the different production mechanisms. It is emphasized that taking into account NN ISI effects affects the magnitude of the cross sections significantly leading to a reduction of a factor 10 (or even more) in some cases. $\bullet$ The total and differential cross sections of the a$_{0}$-meson production in the reaction pn $\rightarrow$ ppa$^{(-)}_{0}$ have been evaluated. The dependence of these cross sections on the specific parameters of he a$_{0}$ meson such as position of the resonance, its width, branching ratio is investigated.
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